1. Field of the Invention
The present invention relates generally to nuclear power plants and, more particularly, to a method of operating a nuclear power plant at multiple power levels during the course of a fuel cycle.
2. Description of the Related Art
The design and operation of nuclear power plants in the United States are highly regulated. The federal regulations regarding the licensing of nuclear power plants are set forth at 10 C.F.R. § 50. In applying for a license on a nuclear power plant from the Nuclear Regulatory Commission (NRC), one must set forth various operating parameters of the power plant, including the thermal power level at which the reactor will be operated and above which the reactor will not be permitted to be operated. In determining what will be the operating power of a nuclear reactor for purposes of obtaining a license, one must perform calculations that assume multiple simultaneous worst-case scenarios, even though many of such scenarios cannot, as a practical matter, exist simultaneously. As a general matter, therefore, power ratings of nuclear reactors in the United States are conservative with respect to the actual power capacity of such reactors.
As an additional matter, such calculations typically assume that certain conditions within the reactor are at their worst-case values, i.e., maximum or minimum values, at all times during the course of a fuel cycle of the reactor, when in fact such values can vary in a known fashion from the beginning of cycle to the end. Accordingly, such nuclear reactors operate at power levels below what could be achieved if the values of such conditions were considered as being variable and not fixed at their worst case levels.
Two examples of such variable values of reactor conditions are the heat flux peaking factor (FQ) and the enthalpy rise peaking factor (FΔH). It is known that FQ is typically at a maximum at the beginning of a fuel cycle and decreases with the depletion of the fuel rods of the reactor. It is also known that FΔH typically starts at an initial value and increases slightly in the initial stages of a fuel cycle but thereafter decreases with depletion of the fuel rods. Calculations that are performed in order to determine a power level at which a reactor will be licensed to operate are based on the assumption that the values of FQ and FΔH are fixed at their maximum levels, although such values are at a maximum for only a relatively short period of time during the fuel cycle.
A nuclear power plant is generally said to comprise a reactor and the Balance Of Plant (BOP), with the BOP including all of the apparatus that interacts with the reactor in order to generate electricity. It is also known that the various components of the BOP are designed to operate at a given operating level, but typically include an additional margin, whether as a factor of safety, a design excess in order to comply with rating requirements, or for other reasons. It is also known that various environmental factors can affect the performance of a nuclear power plant. For instance, a cooling tower may be designed to have a certain rated capacity at 80° F. and 90% relative humidity, and may be designed with a margin of an additional 2%. Accordingly, the cooling tower can operate at another 2% above its rated capacity at 80° F. and 90% relative humidity. On a winter day with a temperature of 20° F. and 10% relative humidity, however, the cooling tower may be operating at only 90% of its rated capacity to meet the cooling needs of the power plant. Accordingly, on such a winter day the cooling tower potentially could provide an additional 12% capacity. It thus can be seen that the performance conditions of the various components of the BOP, as well as the process parameters of the environment, can cause the BOP to have an additional aggregate capacity above and beyond what is needed when the reactor is operating at its rated power level. It thus would be desirable to take advantage of the excess capacity of the BOP, perhaps in conjunction with reductions in FQ and FΔH below their maximum values with the depletion of the fuel rods.